Rheumatoid arthritis (RA) involves chronic inflammation and proliferation of the synovium, which is in part due to defective apoptosis of pathogenic effector cells. Inappropriately low apoptosis likely contributes to persistent synovial cell proliferation in rheumatoid arthritis. In animal models of inflammatory arthritis, agonist activation of the Fas Receptor improves disease, however a challenge is to specifically induce Fas-mediated apoptosis only in pathogenic cells. RA patients have high levels of Vascular Endothelial Growth Factor (VEGF) produced by synoviocytes, not found with normal cells. Our application will exploit the high local concentrations of VEGF secreted by inflamed synovium to directly target a Fas agonist to induce apoptosis at those sites. We developed a novel fusion protein with Fas ligand linked to a VEGF binding domain (R1FasL). We show that R1FasL triggers apoptosis and is cytotoxic only with clustering by VEGF. Our application will examine VEGF effects on inflammation and apoptosis in inflammatory arthritis and utilize the novel R1FasL fusion protein as a treatment for inflammatory arthritis to determine if we can selectively eliminate pathogenic cells in areas where VEGF is produced. Our specific aims are: 1) Determine VEGF and VEGF receptor expression in the murine inflammatory arthritis models SKG and collagen induced arthritis (CIA). 2) Determine cytokines induced by VEGF with or without Fas ligand stimulation of synoviocytes, macrophages and osteoclasts from mice with inflammatory arthritis. 3) Determine the effect of VEGF on Fas-mediated apoptosis of synoviocytes, macrophages and osteoclasts. 4) Determine the effect of R1FasL treatment using the inflammatory arthritis models SKG and CIA. PUBLIC HEALTH RELEVANCE: Rheumatoid Arthritis is a chronic and debilitating inflammatory disease and despite significant advances in treatment, patients continue with active disease due to a lack of response or side effects with available therapies. Our application investigates the role of VEGF or vascular endothelial growth factor in pathogenesis of this disease and utilizes the abnormal production of VEGF by synovial cells to selectively remove these pathogenic cells. Our studies will further our understanding of disease pathogenesis in inflammatory arthritis and examine a novel type of therapeutic in animal models for this disease.